martin



T. G. MARTIN.

AUTOMATIC PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM.

APPLICATION FILED OCT. 21' IQII- H ENEWED MAY II. ISIS. 1,312,558.

Patented Aug. 12, 1919.

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17 OE/VEYS T. G. MARTIN.

AUTOMAHC PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM.

APPLIVLATION FILED OCT.2I.19H- RENEWED'MAY 1?. 19m.

1 3 1 2, 5 5 8 4 Patented Aug. 12, 1919.

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THE COLLWW'A PLANOIIIIAPH 10., WASHINGTON. n. c.

T. G. MARTIN.

AUTOMATIC PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM- APPLICATION men out.2l, l91lneuzwcn MAY 11. ms.

1 3 1 2, 55 8 V Patented Aug. 12, 1919.

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WITNEfiSES MENTOR.-

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TIII! cnumnu PLANIICIRAIII cm. WASHINGTON, n. r.

UNITED STATES PATENT OFFICE.

TALBOT G. MARTIN, OF CHICAGO, ILLINOIS, ASSIGNOR TO AUTOMATIC ELECTRICCOMPANY, OF CHICAGO. ILLINOIS, A CORPORATION OF ILLINOIS.

AUTOMATIC PRIVATE-BRANCH-EXCHANGE TELEPHONE SYSTEM.

Specification of Letters Patent.

Patented Aug. 12, 1919.

Application filed October 21, 1911, Serial No. 655,985. Renewed May 17,1919. Serial No. 297,957.

To all whom it may concern:

Be it known that I, TALBOT G. MARTIN, a citizen of the United States ofAmerica, and resident of Chicago, Cook county, Illinois, have invented acertain new and useful Improvement in Automatic Private Branch-ExchangeTelephone Systems, of which the following is a specification.

My invention relates to automatic telephone systems, and moreparticularly to telephone systems comprising a main auto matic exchangeand an automatic private bram-h exchange. In private branch exchangesystems it is often desirable that the private branch exchange, which isusually represented by a single number, have a plurality of trunk lines,and by calling the number of this exchange an idle trunk line in a groupis selected.

One of the objects of my invention is to provide an improved rotaryselector, which selector is provided with a plurality of trunk terminalsarranged in different levels, and two or more groups of trunk lineswhich extend to private branch exchanges terminating in the same levelof this rotary selector. In connection with an automatic private branchexchange it is likewise necessary that this rotary selector be providedwith means for repeating impulses in order to extend the call throughthis branch cxhange. This rotary selector operates in a manner similar.to that of a rotary connectorthat is, after the wipers have been raisedto any level by impulses representing one digit, they do not begin torotate automatically as in the ordinary selector switch; but in responseto the impulses for the second digit, the wipers are rotated on to thecontacts corresponding to that digit. If the first of the group ofcontacts corresponding to this digit is busy, the wipers will beautomatically rotated to an idle contact. Among the novel features ofthis switch is the provision of two private banks of contacts and twoprivate or testing wipers. The guarding potential on the contact; of oneof these banks will cause the contact arms to rotate past thecorresponding trunk, while a guarding potential upon both contacts willcause the arms to stop upon that trunk, but will prevent the completionof the talkin circuit.

These and other 0 jects of my invention will be more clearly understoodby reference to the accompanying drawings, in which- Figures 1, 2 and 3show a complete connection between a calling substation A and i calledsubstation A in a system embodymg the principles of my invention.

The line of the calling substation A terminates in a main automaticexchange, while the substation A is located at a small branch exchange.The main automatic exchange is a well-known type comprising subscribersindividual or line switches, selectors and connectors. The branchexchange comprises subscribers individual switches, selectors andconnectors. The connection shown is extended through the subscribersindividual switch C, a first sclector E and a combined selector andrepeater F at the main exchange to a trunk line leading to a connector Hat the branch exchange, through the medium of which the connection iscompleted with the called line. The selector-repeater F is preferablyused exclusively for calling branch exchanges and it, together with anumber of other similar switches, is accessible through some particularlevel of the first selectors E. The remaining levels of the firstselectors may be connected with ordinary second selectors in the usualmanner for the purpose of extending connection through the main exchangeto subscribers lines which terminate directly therein. At L (Fig. 3)there is shown a ringing current generator and at M, M and M busysignaling machines are represented. Each exchange is shown provided witha battery B for supplying current for operating the central ofliceswitches and for talking purposes.

The automatic substations may be of any suitable or approved type. Asshown herein, the substation A comprises the usual receiver 2,transmitter 3, switch hook 4, ringer 5 and condenser 6. Since it is anautomatic substation, it is also provided with an automatic callingdevice of the Well-known type comprising a pair of impulse springs 7 and8 and a toothed impulse wheel 9, which latter is controlled b thesubscriber through the medium of a dial (not shown) provided with fingerholes. The mechanism is so arranged that as the dial and impulse wheelare rotated forward by the subscriber, the impulse springs are notoperated; but as the dial returns to normal position, said springs areseparated momentarily a number of times, corresponding to the digitcalled. In order to prevent the resistance of the substation apparatusfrom interfering with the cliicient operation of the relays at thecentral ofiice, there is secured to the same shaft to which the impulsewheel 9 is secured an arm 197 which, whenever the dial and impulse wheelare turned, permits the spring 198'to engage the spring 199. Theengagement of these springs establishes a short-circuit around thetransmitter and receiver, and since this short-circuit endures as longas the impulse springs 7 and 8 are bein operated to transmit impulses tothe Contra office, said impulses are prevented from passing through thereceiver and transmitter at the substation. When the impulse wheelreturns to normal position, and after the last impulse is delivered tothe central ofiii-e, the arm 197 separates the springs 198 and 199 torestore the receiver and transmitter to operative condition for talking.

The line switch C and the master switch I) are of the eneral type ofline and master switches dlsclosed in British Patent N 0. 26,301, of1906, to R. W. James, but are of the particular form shown in Britishpatent to T. G. Martin, No. 1419 of 1910. As herein represented the lineswitch C comprises, ainong other details, a plunger (not shown) which isattached to the end of a so-called plunger arm 10, which latter iscontrolled by the plural-wound magnet 11. Besides controlling theplunger arm 10, the magnet 11 also controls the relay armatures 12 and13 and comprises four windings, namely, a pull-in winding 14, a holdingor cut-off windin 15, a line Winding 16 and an auxiliary win ing 17. Thelateral projection 18, near the center of the core of the magnet and bymeans of which said magnet is mounted upon the bracket 19, divides themagnetic circuit of the magnet into two parts, so that the windings uponone end of the core do not have any effect upon the armatures on theother end. Of the two windings upon the upper end of the magnet, onlythe winding 14 is strong enough to attract the lunger arm 10 from itsnormal position. Although, the winding 15 is not strong enough tooperate the arm 10, it is strong enough to hold it in its operated.position after it has once been pulled down. When the plunger arm 10is'attracted by the magnet 11, the plunger of the switch is forced intoa group of contact springs 20, 21, 22, 23, 24:, 25, 2-6 and 27,, forcingthem into contact in pairs. Although only one set of springs 20-27 isshown, each switch is provided with a plurality of such sets, each setform ing a terminal of a separate trunk line leading to a selector E.Each trunk line is multipled through the corresponding contacts of allthe switches of a group which is controlled by the master switch D,while the lids conductors of the substation A are connected in multi JlGto the springs 20 and 22 of all of the di 'erent sets in its own switch.The plungcrs of all the line switches of the group which is controlledby the master switch ,I) engage a so-called plunger shaft (not shown),and through the medium of said master switch are normally maintainedopposite the terminals of an idle trunk lino. 'lhc master switchconsistsessentially of a motor magnet 28 for rotating the ratchet wheel29. The ratchet wheel 29 is connected with the plunger shaft in suchmanner that a rotary motion of the ratchet wheel gives to the plungershaft a reciprocating motion to carry the idle plungers back and forthin front of their trunk terminals. To the plunger shaft there is secureda locking plate 30 provided near its outer edge with a number ofopenings which are adapted to be engaged by a pin 31 upon the end of thearmature 32 of the relay 33. The openings in the plate 30 are so spacedthat the pin 31 can engage one of them and allow the armature to resumeits normal position only when the plungers of the idle line switches aredirectly opposite the terminals of a trunk line. The master switch alsoprovided with a bank of contacts comprising a common segment 34 and anindividual contact a for each trunk line to which the line switches haveaccess. The wiper 35 always maintains the segment 34 in electricalconnection with the individual contact a of the trunk line before whichthe plungers of the idle line switches are being held by the masterswitch.

The selector E is of the general type of selector switches disclosed inUnited States Letters Patent No. 815,321.. granted to Keith. Ericksonand Erickson March 13. 1996, the circuits being modified,-however, asshown in British Patent No. 1419 of 1910 referred to above. in order tooperate in a two-wire system-that is, a system in which the centraloffice apparatus is controlled by the calling subscriber over the twosides of the line in series. As herein represented, the selector Ecomprises a bank of contacts arranged in rows or levels, which contactsare adapted to be engaged by a set of wipers 36, 37 and 38 carried upona vertically and rotatably movable shaft (not shown) which is controlledby the so-called vertical and rotary magnets 39 and 40. The usual sideswitch comprising the wipers 4-1. 4-2, 43 and 44 is controlled by theprivate magnet 45 in a manner well known in the art. Means for restoringthe switch to normal position are provided in the release magnet 46. Inthis instance the release magnet is adapted to restore the switch tonormal position immediately upon energizing, as shown in United StatesLetters 'l-atent No. 815,176, granted to Keith, Erickson and EricksonMarch 13, 1006, for connector switches, rather than by dei nergizing asshown in the selector patent hereinubovc referred to. The springs 17 arepermitted lo engage only when the switch shaft is raised one or morestep from its lowest or normal position. The operations ot' the switchare controlled by the calling subscriber through the medium ofthedoulilcuvouinl line relay 4.8. The relays ll), 50 and 51 areslow-acting rclaysthat is, relays which debncrgizc slowly alter theirenergizing circuits have l.-ccn broken. The desired action of theserelays may be accomplished by providing a ring of copper around one endof the core. The contacts 52, 53 and 54 are assumed to be a set ofcontacts in the first level of the selector bank and are the terminalsof a trunk line lead ing to the :-ielector-rcpeater F. The contacts 555G and 57 represent a. set of contacts in the second level and Form theterminals of a trunk line which may lead to an ordinary second selector.

The general construction of the selector-- repeater F is practically thesame as that of selector E, the selector-repeater F has four oration,however, being somewhat different. Instead of only three wipers. as inthe selector E, the selector-repeater has four wipers, namely, the twoline wipers 58 and 59 and two private or testing wipers 60 and 61. Thereis no third conductor in the trunk line leading to the connector Hcorresponding to the conductor 11G (Figs. 1 and 2), and the contaetwhich are engaged by the wipers 60 and 61 are simply multipled with thecorresponding contacts in the banks of the other switches F which haveaccess to the same trunk lines as the switch shown in the drawings. Thedifl'erence in the mode of operation of the selectors E and F is asfollows: In the selector E the wipers are adapted to be raised to anylevel of the bank contacts by a certain number of impulses transmittedthrough the line relay 4:8, and upon the cessation of these impulses thewipers are automatically rotated onto the first set of idle contacts inthis level. Thus, in the selector E all of the trunk lines which areconnected to contacts in any given level are accessible by calling onedigit. In the selector F the wipers are raised to any desired level by anumber of impulses transmitted through the line relay 62 in practicallythe same manner as in the selector E. The wipers of the selector F,however, do not begin to rotate automatically upon the cessation of theimpulses through the line relay. After the wipers have been raised toany desired level, they may be rotated onto any desired set of contactsin that level by another set of impulses through the line relay. Uponthe cessation of this second set of impulses, the wipers of the selectorF will remain upon .the contacts onto which they have been rotated itthe trunk line cennecled to these contaiis is idle. l i" this '3 runl;line is busy, however, the wipers will lie a ioinatically rotated ellthem, and will coniiriue to rotate until the contacts of an idle trunkline are rr'achcd. or until a point is reached where the contactsengaged by th two private wipers (it) and (ii are conneclwl together.\Vith this arrangmi'icnt it will be evident that a plurality of groupsof trunk lines may be connected to each lc cl ol' hau contacts oi theselector F, and an ialle line in any one of these groups may be selectedby calling two digits upon the su itch, these two digits correspondingto the position in the bank of the first trunk line of the group. Thecontact-1 which are engaged by the wipers (l0 and G1 and correspoinlinglo the last trunk line in every group are connected together. l i henthe wipers are rchirg; For an idle tzcnlc and reach a pr-ll'liili wherethe wipers til) alvl ll engage contacts which are thus cmiucctcdtogether. the wipers will come to rest regardless oi whether the trunkline is busy or idle. I the trunk line i busy. no cmiaection will becompleted therewith when the wipers 58 and 59 come to rest upon itscontacts. The selector F. besides acting as a selector, also acts as arepeater to receive impulses from the calling: substat on and repeatthem around the condensers (l?) and 64 to the trunk line with which ithas made connection. The line relay ($5 3 is onnected with the trunkconductors 65 and (it; through the cont acts of rcvcr This relay isprovided with two windings (l8 and 69, and it is necessary that both ofthese windings be energized and in the same direction before itsarmature will be cperated. tcrrupting the circuit of the rotary magnet125 to cause the wipers to rotate in search of an idle trunk linecomprises a relay 13-1, the circuit of which is controlled by thearmature of the rotary magnet through the medium of the contact 133.

The connector H is of the general tvpe of connector switch disclosed inUnited States Letters Patent No. 815,176 previously referred to, but,like the selectors, is modified to operate in a wo-wire system. Like theselectors, the connector is provided with a shaft (not shown) carryingthe wipers 70, 71 and 72 and controlled by the vertical and rotarymagnets 73 and 74. The usual side switch is controlled by the privatemagnet 75 in the usual manner. At 76 there is shown a ringing relaywhich is provided for the purpose of connecting the ringing currentgenerator to the called. line to signal the called subscriber. Thetalking circuit through the connector is divided into two sections,which sections are inductively connected by the condensers 7 8 and 79.

The substation A and the line switch C clay GT. 100

The means for automatically in- 105 L'flu in all respc ls llle same asthe sulislation .unl ilnline wwiteh l ming given a general descriptionof the apparatus, it will now he explained in detail how the subscriberat substation A may obtain connection with the branch exclmngesubstation 1'1, llli number ol' which latter will he assiuued to heli'iii flll. The number 155 signifies the common number of a pluralityof trunk lines leading to the branch exchange, while the niunher 20signilies the number oi the subi-ztation A in the branch exchange. Thus,it has been assumed that the first trunk line of the group leading tothe branch exchange to which the substation A belongs is connected tothe liftli. set of contacts in the filth level of the banks of theselector F. In the draw ings it has been assumed that the trunk lineshown is (his lirst trunk, and that there are lhree trunk lines in lliegroup. The prirale hank contact: of all these three lines are shonn, thecontacts 3'2 and t-i belonging l the last trunk line being connectedtoge 'heit When [he willing subs -i-ibcr removes his receiverpreparalory to making a call, the switch hook rises, permitting thesprin to engage the spring 81, whereby a circuit is closed through theline relay 16 of the line switch C. This circuit extends from ground Gthrough the springs and 86, line conductor 90, hook switch springs 80and 81, impulse springs S and 7, receiver 2, transmitter 3, line 91,springs 88 and 87 and the winding 16 to the battery lead 92, thencethrough battery B to ground G. The wind ing 16, upon energizing,attracts the armaturn 13, which operates to complete a circuit fromground G through the springs 85 and 34', pull-in winding 11, auxiliarywinding 17, contact point 93 and armature 32 to the bat tery lead 92.The winding 14, upon encr gizing, attracts the plunger arm 10 and thecut-off armature 12. The armature 12 opcrates to disconnect the lineWinding and ground G from the line, While the plunger arm 10 causes theplunger to force the springs 2027 into contact, as shown. The engagementof the springs 20 and 22 with the springs 21 and 23, respectively,extends the line conductors and 91 to the selector E, whereupon its linerelay 48 becomes enerized over a circuit extending from ground 1 throughthe lower winding of said relay, side switch wiper 42, springs 23 and22, thence to and through the substation A and back over the other sideof the line through the springs 20 and 21, side switch wiper 41 and theupper winding of the relay 48 to the battery lead 92. The relay 48, uponenergizing, closes the circuit of the relay 49. The relay 49, uponenergizing, completes a circuit from ground G through the springs 94, 25and 24 and the winding 15 of the line switch C to the battery lead 92.This energizalion ol the winding 15 is for the purpose of maintainingthe armature 12 and plunger arm ll) in their operated positions al'lerthe circuit of lhe winding 14- is broken by the falling hack of thearmature 13, when the line winding Hi is disconnected from the line. Theauxiliary winding 17, which is energized in series with the pull-inwinding 14, is short-cireuited at the contact when the plunger armreaches its operated position, and is therefore energized onlymomentarily. This momentary energizal'iion, however, serves to maintainthe armature 13 :u-tracted for an instant after the wimling 16 is deiuergized, so as to insure that the circuit of the winding 14. shall notbe broken bel'ore the holding winding 15 has had time to he energized.The euergization oi the relay i at the sllerl'pr also :sxi'euds aguarding poieu'ial from ground ll through the springs it, ill and illand (o'er the munlurtor in; to (he connector private bank ronlnels ol"the railing line,

he Closure oi the springs 26 and 27 upon liroperation of the line snitchcom letes a circuit from ground (i through said springs 26 and 27,contact point 97, Wiper 35, segment 34 and relay 93 to the battery lead92. The relay 98, upon energizing, closes an energizing circuit throughthe relay 33. The relay 33, upon energizing, withdraws the pin 31 fromthe locking plate 30 and closes the circuit of the motor magnet 28. Thiscircuit extends from ground G through said magnet 28, interrupterspringscontact and arn'iature 32 to the battery lead Since this circuitincludes the interrupter springs 99, the magnet 28 will operatecontinuously in a manner similar to that of a buzzer to advance theplunger shaft step by step as long as the armature 32 engages thecontact 100. After the plun er shaft and idle plungers have been movec ashort distance, the wiper 35 passes off the contact 97, and if the nexttrunk line after the one seized by the switch C is idle, the relays 98and deiinergize. The relay 33 being denergized, the armature 32 willfall back and break the circuit of the magnet 28, when the next openingin the plate 30 comes directly under the pin 31 and the plungers of theidle line switches will be brought to rest in front of the correspondingtrunk line. If the first trunk line after the one seized by the switch Cis busy, the wiper 35 will find the corresponding contact in the masterswitch bank rounded. The relays 98 and 33 will therefgire remainenergized while the next opening in the plate 30 is passing under thepin 31, and the idle plungers Wlll be carried past the busy trunk lineto an idle on c. The separation of the armature 32 from the contactpoint 93 while the relay 33 is energized disconnects the battery fromthe pull-in windings of all these line switches.

till

This is to prevent any line switch from being operated While its plungeris being moved to an idle trunk by the master switch.

Connection having been extended to the selector E, the callingSlllISCl'lllCI now operates his calling device for the first digit 1 ol'the called number. This operation of the calling device short-circuitsthe receiver and the transmitter by the engagement of the springs 198and 199, and momentarily separates the substation impulse springs 7 and8 once, thereby allowing the selector line relay 48 to be momentarilydcenergized. The relay 49, being slow acting, does not have time todeiinergize during the momentary interruption of its circuit by therelay 48. The dei nergization of the relay 48 therefore results in theclosure of a circuit from ground G through the spring 102 and its backcontact. spring 103 and its front contact, relay 50 vertical magnet 39and the side switch wiper 44- to the battery lead 92. T he verticalmagnet upon energizing, raises the switch wipers one step to a positionopposite the first level of bank contacts. The relay 50, which isenergized in series with the vertical magnet 39, is a slow acting relayand dee'nergizcs shortly after the circuit of said magnet is broken. Ifmore than one impulse had been transmitted through the vertical magnet,the relay 50 would not have deiinergized until after the last impulsehad been delivered. The relay 50, upon energizing, completes a circuitfrom ground G through the springs of said relay and through the privatemagnet 45 to the battery lead 92. The private magnet 45, upon energizingand deenerg'izing causes the side switch to pass from first to secondposition. The side witch Wiper -14. in second position. disconnects thebattery from the vertical magnet 39 and completes a circuit from groundG through the interrupter springs 104-, rotary magnet 40, relay 51 andthe side switch wiper 44 to the battery lead 92. Since this circuitincludes the interrupter springs 104, the rotary magnet will operate ina manner similar to that of a buzzer to rotate the switch shaft step bystep as long as the side switch remains in second position. If the firsttrunk line in the first level is idle, the side switch will be trippedfrom second to third position by the action of the armature of therotary magnet upon the armature of the private magnet the first time therotary magnet is energized, and the wipers 36, 37 and 38 will come torest upon the contacts of said first trunk line. It this first trunkline is in use, however, having been seized over its multiple contactsby some other selector similar to the selector E. the wiper 37 will findthe. contact which it engages provided with a guarding ground potential.An energizing circuit will therefore be completed. from said guardedcontact disconnect the line relay 48 from the line and extend theconnection through the wipers 36 and 38 and over the conductors 65 and66 to the selector F (Fig. 2). The line relay 62 of the selector Fthereupon becomes energized over a circuit extending from ground Gthrough the lower winding of said relay, springs 109 and 108, conductor66, thence to and through the substation A and back over the other sideof the line, trunk line conductor 65, springs 105 and 106 and the upperwinding of the relay (32 through the battery lead 92. The relay 62, uponenergizingi completes a circuit from ground G through the spring 111 andits front contact and the relay 112 to the battery lead 92. The relay112, upon energizing, provides a holding circuit for the relay 49 of theselector E to maintain said relay energized after its originalenergizing circuit is broken by the falling back of the relay 48 when itis disconnected from the line. This holding circuit extends from groundG through the springs 115. conductor 116, contact 52, wiper 37. sideswitch wiper as, spring 117 and its back contact and the relay 49 to thebattery load 92. A guarding potential is also extended from ground Grover the circuit just traced to the selector private bank contact 52 andthence to the corresponding contact in the banks of all the selectorswhich have access to this trunk line. A short interval elapses betweenthe time when the side switch of the selector E passes to third positionand the time when the relay 112 of the selector F energizes to extendthe guarding potential back to the private bank contacts of the trunkline. During this interval the guarding potential is provided by therelay 51 of the selector E. This relay is energized in series with therotary magnet 40 and being a slow acting relay, remains energized for120 a short time after the side switch has passed to third position. Inits energized position the rela 51 extends a connection from ground 1through the springs 118 and 117, side switch wiper 43 and the wiper 37to the selector private bank contacts. The relay 51, of course,de'elnergizes in time to close the holding circuit of the relay 49before it has time to deenergize.

The; subscriber at the calling substation now operates his callingdevice for the second digit 5, thereby momentarily interrupting thecircuit of the relay (52 of the selector i live time. Since the rela 112is slow acting like the relay 15) of tie selector E, each time the relay62 deenergizes a circuit is closed from ground Gr through the spring 111and its back contact, spring 119 and its front contact, relay 120,vertical magnet 121 and the side switch wiper 122 to the battery lead92. The five impulses transmitted over this circuit cause the verticalmagnet to raise the switch shaft live steps to raise the wipers to aposition opposite the fifth level of bank contacts. The relay 120, whichis included in circuit in series with the vertical magnet, is a slowacting relay and remains energized during the entire time the verticalmagnet is operating. In its energized position the rc lay 120 completesa circuit from ground G through the spring 123 and its front contact andthe private magnet 121 to the battery lead 33. When the relay 120deenergizes after the lust impulse is delivered to the vertical magnet,it breaks the circuit of the private magnet 121, which thereupondeenergizes and causes the side switch to pass from first to secondposition. The side switch wiper 122, in passing from first to secondposition, transfers the battery connection from the vertical magnet 121to the rotary magnet 125. Thus, when the calling subscriber operates hiseallin device for the next digit 5, the operation 0% the line relay G2,in response to the impulses for said digit, transmits a series of fiveimpulses over a circuit extending from ground G through the spring 111and its back contact, spring lit) and its front contact, relay 120.springs 12(3, rotary magnet 125 and the side switch wiper 122 to thebattery lead 92. The magnet 125, operating in response to theseimpulses, rotates the shaft five steps to carry the wi iers 58, 59, 60and 61 onto the first trunk line of the group No. 155, which in thiscase is assumed to be the trunk line shown leading to the connector H.If this trunk line is idle, the relay 120 operates in response to theimpulses for this digit in the same manner as explained for the previousdigit, to cause the private magnet to advance the side switch onestep-that is, from second to third position after the last impulse isdelivered. If this trunk line had been busy, however, the wiper 61 wouldhave found the contact which it engaged Jrovided with a guarding groundpotentia This guarding potential would have provided an energizingcircuit for the relay 127, said circuit extending through the shaftwipers 61, side switch Wiper 129 (this wiper being in second position)and the rela 127 to the battery lead 92. The relay 12 upon energizing,completes a circuit from ground G through the springs 130 and theprivate mag net 124 to the battery lead 92. This circuit maintains theprivate magnet 12 1 energized after the relay 120 is dei nergized afterthe last impulse is delivered to the rotary magnet by the line (32. Theprivate magnet 124-, being locked up, holds the side switch in secondposition, and the relay 127, being nergized, the deencrgization of therelay 120 completes a circuit from ground (1 through the spring 123 andits back contact, springs 131, springs 132, springs 126, rotary magnet125 and the side switch wiper 122 to the battery lead The rotary magnetenergizes upon the completion of this circuit and operates to advancethe shaft wipers one step to the next trunk line, and also completes acircuit from ground G through the contact 1 53 and the relay 134. to thebattery lead 92. The relay 13-1, upon energizing, interrupts the circuitof the rotary magnet at. the springs 13:2. The rotary magnet thereupondefiner ms and in turn breaks the circuit. of y 131. The relay 131, upondeiincrgrainy, again closes the circuit of the rotary magnet. The relay127 will remain energized as long as the wiper G1 continues to ei'igagegrounded contacts of busy trunk lines, and the rotary magnet willcontinue to advance the wipers step by step until the wiper 61 finds anon-grounded contact and permits the relay 127 to deenergize, or untilthe wipers (30 and (31 engage the contacts 82 and 83, which areconnected together. These contacts 82 and 83, as has been explained,belong to the last trunk line of the group No. Of course, if this trunkline is idle, the contacts 82 and 83 will not be grounded and the relay127 will de'energize and permit the wipers to come to rest thereon inthe same manner as for any other idle trunk line. It this trunk line isbusy, however, the contact 82, as well as the contact 83, will begrounded. The ground upon the contact 83 would cause the wipers tocontinue their autmnatic rotation but for the fact that the ground fromthe contact 82 completes a circuit extending through the wiper (30,springs 234 and 135, springs 136, relay 137 and the side switch wiper138 to the battery lead 92. The relay 137, upon energizing, breaks thecircuit of the rotary magnet at the springs 12G, notwithstanding thefact that the relay 127 remains energized. The wipers 58, 59, 60 and 61,therefore, come to rest upon the contacts of this busy trunk line, butno connection is completed between the calling line and this trunk linebecause the private magnet 124 remains energized and holds the contacts139 and 110 open. The relay 137 upon ener izing, forms a locking circuitfor itself, in ependently of the contact 82. This circuit extends fromground G through the springs 130, springs 1 11, 142 and 135, 136, relay137' and the side switch Wiper 138 to the battery lead 92. This lockingcircuit is to prevent the selector F from com 'iletiiu; connection withthe trunk line in case the guarding potential is removed from the contaet; 82 after the selector 1* has attenq'itetl. to make connectiontherewith and before the calling subscriber has hung up his receiver.The relay 13?, .in its energized position, also completes a. connectionfrom the busy sig hating ltlnt'hlllo M through the springs 143,condense) (A and thence over the heavy eonductors to the callingsubstation A, whereby the calling subscriber is given the busy signal toindicate that all of the trunk lines leading to the desired branchexcl'iange are in use. The return circuit for the busy signalingcurrent, after passing through the substation, is over the lineconductor 91, thence through the selector E and over the trunkeoiuluctor 3 and througl'i the upper winding;' of the line relay (i2 oithe selector l to the battery lead 1);, and thence back to the busysignaling machine M. Upon receiving the busy signal, the callingsubscribe-r, by hanging up his receiver, releases the switches C, l!)and F in the same manner as when a complete connection has beencompleted and which will be described later.

When the wipers of the selector F come t rest upon the contacts 01' anidle trunk line and the private magnet 124 dcenergizes, as has beenexplained, the side switch passes to third position and the connectionwith the trunk conductors 145 and 146 is completed by the closure of thecontacts 139 and 110. The side switch wiper 12%), upon passing. to thirdposition, extends a guardlug potential from ground. G through said wiper129 and the private Wiper 61 to the private. bank contact of the seizedtrunk line in the banks of all the switches which have access thereto.The side switch Wiper 147 upon reaching third position, completes abridge across the trunk conductors 1-15 and 146, whereupon the linerelay 148 of the connector H becomes energized over the circuitextending from ground G through the lower winding of said relay, springs149 and 150, conductor 1 16, wiper 58, side switch wiper 147, impedancecoil 151, winding 69, springs 152, wiper 59, conductor 145, springs 153and 154 and the upper winding of the relay 148 to the battery lead 155.The relay 118. upon energizing, completes the circuit of the relay 156.At the selector F the currcntflowinpr through the winding 69 of therelay 67 is opposed by a current flowing through the winding 68 o er acircuit extending from ground G through the springs 157 and the winding68 to the bat tcry lead 92, and the relay is not operatively energized.The circuit of the winding 68 is closed as soon as the switch shaftleaves is normal position, but, as has been explained, the relay 67 cannot be operated by the energization of one whaling alone. When thesubstation calling device is operated for the fourth digit, the circuitof the line relay 62 of the selector F is again broken twicemomentarily. The separation of the springs by the (lei nergizatiou ofthe relay 62 at this time opens the bridge across the trunk conductors145 and 116, thereby breaking the energizing circuit of the relay 1&8 ofthe connector 1!. The relay 148. upon (lei nergizing, completes acircuit from ground 2 through the spring 158 and its back contact,spring; 159 and its trout contact, relay 160, vertical uran'net 73 andthe side switch wiper 161 to the battery lead 155. Since the digitcalled is 2, the vertical magnet receives two impulses over this eircult and operates to raise the switch shaft and wipers two steps. Therelay 160, being a. slow acting: relay, operates to maintain the circuit[from ground (2" tlu'ough the springs 1t2 and 163 and the private magnetto the battery lead 15.3 closed while the vertical magnet is operating.After the last impulse delivered to the vertical magnet, the relay 160deiinergizes and in turn permits the private magnet 75 to deenergize toallow the side switch to pass to second position. At the selector F,each time the relay 62 deiinergizes to repeat an impulse to the relay14:8 of the connector, a circuit is closed from ground G through thespring 111 and its back contact, spring 119 and its front contact, relay120. relay 166 and the side switch wiper 122 to the battery lead 92. Theenergization of the re lay 120 at this time is functionless and causesthe private magnet to open the con tacts 139 and 1L0 while impulses arebeing); repeated over the trunk conductors 1'15 and 146. This operationof the private magnet has no effect on the side switch because it hasreached the limit of its travel. The relay 166,, being slow acting.remains in its energized position during the entire time the relay 62 isoperating in response to the impulses received from the substation. andin its energized nosition the relay 166 shortcircuits the impedancecoil151 and the winding 69 of the relay 67 so as to remove theresistance from the circuit of the connector line relay While it isbeing operated.

When the substation calling device is operated for the last digit 0, theline relay 62 of the selector F operates in response to the impulsesreceived from the substation to repeat ten impulses to the line relay148 of the connector H. Each time the relay 14S deiinergizes in responseto these impulses it completes a circuit from ground G through thesprings 15 8 and 159, relay 160. springs 167, rotary magnet 74 and theside switch wiper 161 to the battery lead 155. The rotary magnet 74therefore operates to advance the wipers 70, 71 and 72 ten steps ontothe contacts of the desired line. If this line is idle, the relay 16operates in the same manner as for the previous digit to cause theprivate magnet to itllvitih e the side switch to third position afterthe last impulse is received. The side switch, upon passing to thirdposition,completes the connection with the called line and said line isprotected by a guarding potential ltxllvlllllllg from groui'id 1 throughthe side switch wiper 168 and the shaft wiper 72 through the eoiuiei-torprivate bank contacts of the called line. From the wiper 72 a circuitalso extends through the ut-off windino 169 of the line switch C to thebattery lead 155. The winding 169, upon energizing, attracts thearmature 170, which disconnects the switch C from the called line andcloses the contact 171 in the talking circuit. The side switch wiper161, upon passing to third position, completes a rirruit from lround G"through the interrupter 173. ringing relay 76, springs 174 and 175 andthe -:iclc switch wiper 161 to the battery lead. The relay 76, uponenergizing, disconnects the calling line from the called line andconnects the ringing current generator L with the called line to signalthe called subscriber. Since the circuit of the ringing relay includesthe interrupter 173, said relay is energized only intermittently so asnot to ring the called subscriber continuously. When the calledsubscriber removes his receiver, or as soon thereafter as the ringingrelay 76 denen gizes, if it happens to be energized at the time, thecalled substation is provided with talking current over a circuitextending from ground G through the side switch wiper 168, lower windinof the relay 176, ringing relay springs 1 7 and 178, side switch wiper179, line 180, thence to and through the substation A and back over theline 181, through the contact 171, wiper 7 O, springs 182 and 183,springs 184, upper winding of the relay 176 and the side switch wiper161 to the battery lead 155. The relay 176, upon energizing, completes acircuit extending from ground G18 through the side switch wiper 168,relay 182 and springs 183 to the battery lead 155. The relay 182, uponenergizing, breaks the circuit of the ringmg relay 76 and forms alocking circuit for itself by way of the springs 184 and 175 and theside switch wiper 161 to the battery lead 155. The shifting of thesprings 150 and 153 out of engagement with their back contacts and intoengagement with their front contacts by the energization of the relay182 transposes the connections between the windings of the relay 148 andthe trunk conductors 145 and 146. This transposition reverses thecurrent in the winding 69 of the relay 67 at the selector F. The relay69 now assists the winding 68 and the relay 67 is operatively energized.The relay 67, upon energizing, transposcs the connections between thewindings of the relay 62 and the trunk conductors 65 and 66, therebyreversing the direction of the current flowing in the calling line.Although this reversal oi? current in the calling line has no particularfunction in the system as shown herein, it is often used for the purposeof operating call registers or supervisory signals in a semiautomaticconnection.

Upon the termination of the conversation, the entire connection isreleased by the hanging up of the receiver at the calling substation.When the receiver is hung up, the circult of the line relay 62 of theselector F is broken. The relay 62, upon denergizing, destroys theenergizing circuit of the relay 112, as well as that of the connectorline relay 148. The relay 112, upon dcenergizing, completes a circuitextending from ground G through the sprin 111 and its back contact,eprin r 119 and its back contact, springs 186 and tie release magnet 187to the battery lead 92. The magnet 187, upon energizing, causes theshaft and the side switch of the selector F to be restored to normalposition, and when the switch shaft reaches its lowest position thecircuits of the release magnet 187 and winding 68 are broken at thesprings 186 and 167. The relay 112, upon denergizing, also opens theholding circuit of the release relay 49 of the first selector E. Therelay 49, upon deenergizing, completes the circuit of the release magnet46 and also breaks the holding circuit of the winding 15 of the lineswitch C. The magnet 46, upon energizing, releases the selector E, andthe winding 15, upon de'c'nergizing, permits the plunger of the lineswitch to be restored to its normal position. The circuit of the magnet46 is broken by the selector shaft when it reaches its lowest positionand separates the springs 47. When the relay 148 of the connector Hdenergizes upon the interruption of its circuit by the relay 62 of theselector F, a circuit is closed from ground G through the spring 158 andits back contact, spring 159 and its back contact, release magnet 188and the springs 189 to the battery lead 155. The magnet 188, u onenergizing, releases the connector switc In the foregoing it has beenassumed that the called line was idle when the connector H madeconnection therewith. If a line is busy it has a guarding groundpotential upon its connector private bank contact, and when the wiper 72is rotated onto said contact, this potential is extended through thewiper 72, side switch wiper 168 (which is then in second position),springs 189" and 190 and the relay 191 to the spring 192 of the privatemagnet relay 160. There being a ground potential upon the spring 192,the private magnet 7 5 does not deiinergize when the relay 160deeinergizes after the last impulse is delivered to the rotary magnet,but remains energized in series with the relay 191. The relay 191, uponenergizing, forms a locking circuit for itself extending from ground Gby way of the springs 193, 194 and 190 so as to prevent said relay fromdecnergizing in case the guarding potential should he removed from theprivate bank contacts. In its energized posit-ion the relay 191 alsocompletes a connection from the busy signaling machine M through thesprings 195, contact 196, side switch wiper 1T9, condenser 79 and thenceover the heavy conductors to the calling substation. It will thus beseen that if a busy line is called, the calling subscriber is given thebusy signal and no connection is completed with the busy line becausethe private magnet 7 5 does not decncrgize after the last digit iscalled, and, therefore, the connection is maintained open on one sid atthe springs 181 and on the other side at the said switch wiper 179,which wiper remains locked in second position.

As shown herein, the trunk lines leading from the sclector-repeater Flead to connector switches in the branch exchange. It will be evidentthat such trunk lines might terminate in selector switches which haveaccess to a. plurality of connectors. The subscribers lin switches C inthe branch exchange may have access to selector switches similar to theselector E (Fig. 1), by means of which the branch exchange subscribersmay select trunk lines leading either to the main exchange or toconnector switches in their own b 'anch exchange.

Ilhile I have illustrated and described my invention in connection witha particular type of automatic telephone system, it is to be understoodthat I do not wish to be limited to such a system, as it is obvious thatif desired the connection between a calling and a called snbscribersline could be established partly manually and that other substitutionsand changes could be made without departing from the spirit of myinvention.

What I claim as my invention is 1. In an automatic telephone system, amain exchange, a plurality of private branch exchanges, a group of trunklines extending from said main exchange to each of said branchexchanges, automatic progressively movable switches at said branchexchanges in which said trunk lines terminate, an automatic switch atthe main exchange having a plurality of contacts arranged in differentlevels, and a plurality of groups of said trunk lines terminating in asingle level of said switch, and means for operating said progressivelymovable switches over said trunk lines through said automatic switch.

2. In an automatic telephone system, a main exchange, a plurality ofprivate branch exchanges, a group of trunk lines extending from saidmain exchange to each of said branch exchanges, automatic progressivelymovable switches at said branch exchanges in which said trunk linestern'iinate, an automatic switch at the main exchange having a pluralityof contacts arranged in different levels, a plurality of groups of saidtrunk lines terminating in a single level of said switch, means foroperating said )rogressively movable switches over saic trunk linesthrough said automatic switch, and means for controlling said switchover two sides of a line circuit in series.

3. In a telephone system, a main exchange, a plurality of private branchexchanges, a group of trunk lines extending from said main exchange toeach of said branch exchanges, a connector switch at said branchexchanges in which said trunk lines termi nate for connecting with thecalled subscribers line, a selector switch at said main exchange, saidselector switch having contacts arranged in a plurality of main groups,a plurality of groups of said trunk lines terniinating in a single maingroup of said contacts of said switch, and means controlled by saidswitch for repeating impulses to con trol the operation of saidconnector switches.

4. In a telephone system,a main exchange, a plurality of groups ofprivate branch exchanges, a group of trunk lines extending from saidmain exchange to said branch exchanges, a connector switch at saidbranch exchanges in which said trunk lines terminate for connecting withthe called subscribers line, a selector switch at said main exchange,said selector switch having contacts arranged in a plurality of maingroups, a plurality of groups of said trunk lines terminating in asingle main group of contacts of said switch, means controlled by saidswitch for repeating impulses to control the operation of said connectorswitches, and means for controlling said switches over two sides of aline circuit in series.

5. In a telephone system, an automatic switch, trunk lines divided intogroups and subgroups, said switch having one motion to select groups anda second motion to select a sub-group and then select an idle trunk linein said selected sub-group, and means in said switch for repeatingimpulses over said selected trunk.

6. In a telephone system, an automatic switch, trunk lines divided intogroups and sub-groups, said switch having one motion to select groupsand a second motion to select a sub-group and then select an idle trunkline in said selected sub-group, means for controlling said switch overtwo sides of a line circuit in series, and means in said switch forrepeating impulses over said selected trunk.

7. In a telephone system, a main exchange, a private branch exchange, aplurality of groups of trunk lines extending from said main exchange tosaid branch exchange, a trunk selector at'said main exchange, saidselector having one motion to select groups and a second motion toselect sub-groups and then select an idle trunk in a se ected subgroup,and means insaid switch for repeatmg impulses over sald selected trunk,

S. In a telephone. system, a mam exchange, a private branch exchange, aplurality of groups of trunk lines extending from said main exchange tosaid branch exchange, a trunk selector at said main exchange, saidselector having one motion to select groups and a second motion toselect sub-groups and then select an idle trunk in a selectedsub-groin), means for controlling said switch over two sides of a linecircuit in series, and means in said switch for repeating lltllflllSOSover said selected trunk.

5'. In a telephone system, a plurality of lines divided into groups, aselector switch having motion in one plane to select groups and rotarymotion to find a line in a selected group, a line relay, :1 slow-actingrelay, means for energizing said slow-acting relay when said line relayis energized, means for partly rotating said switch when said slowaetingrelay is energized and complot-in the rotation of said switch when saids ow-acting relay is deenergized, and means in said switch for repeatingimpulses over said selected trunk.

10. In a telephone system, a plurality of lines divided into groups, aselector switch having one motion to select groups and rotary motion tofind a line in a selected group, a line relay, a slow-acting relay,means for energizing said slow-acting relay, and then denergizing saidrelay when said line relay is energized, means for partly rotating saidswitch when said slow-acting relay is energized and completin therotation of said switch when said s ow-aetin relay is denergized, andmeans in sait switch for repeating impulses over a selected line. i

11. In a telephone system, a plurality of lines divided into groups, aselector switch having one motion to select groups and rotary motion tofind a line in a selected group, a line relay, a slow-acting relay,means for energizing said slow-acting re lay when said line relay isenergized, means for partly rotating said switch when said slow-actingrelay is energized and completing the rotation of said switch when saidslow-acting relay is deenergized, and means controlled by said linerelay for repeating impulses over the selected line,

12. In a telephone system, a plurality of lines divided into groups, aselector switch having one motion to select groups and rotary motion tofind a line in a selected group, a line relay, a slow-acting relay,

means for energizing said slow-acting relay, and then deiinergizin saidrelay when said line relay is energize means for partly rotating saidswitch when said slow-acting relay is energized and COIJJIJlOtlHg therotation oi said switch when said slow-acting relay is deenergized, andmeans controlled by said line relay for repeating impulses over theselected line.

13. In a telephone system, an automatic switch, a bank of line contactsand two banks of private contacts, a )rivate wiper adapted to engageeach of said private contacts, a group of trunk lines having a thirdconductor connected with the corresponding contact in one of saidprivate banks, and means whereby a guarding potential upon one of saidprivate contacts will cause the wipers to be rotated past thecorresponding trunk, while a guarding potential upon both privatecontacts will cause the wipers to stop upon. said trunk.

14. In a telephone system in which the terminals of the trunk lines arearranged in groups and in which the trunks in each group are furtherarranged in sub-groups, a line. conductors for said line, a circuitcloser for said line, a propelling mechanism for advancing said circuitcloser to a group of trunks, and for thereafter advancing the circuitcloser to a sub-group of trunks, test circuits for testing and formaking the trunks busy in the sub-group, means i11- dividual to saidcircuit closer controlled by said test circuits when all the trunks arebusy for rendering said mechanism inoperative, said test circuits beingindependent of the conductors of said line, other lines, and means forextending a connection from any one of said trunks to any one of saidother lines.

15. In a telephone system in which the terminals of the trunk lines arearranged in groups and in which the trunks in each group are urtherarranged in sub-groups, a line, conductors for said line, a circuitcloser for said line, a propelling mechanism for advancing said circuitcloser to a group of trunks, and for thereafter advancing the circuitcloser to a sub-grou of trunks, test circuits for testing and or makingthe trunks in the sub-group busy, means individual to said circuitcloser controlled when all of the trunks are busy for rendering the saidmechanism inoperative, a release device associated with said meehanismfor restoring the said mechanism to operative condition, said testcircuits being independent of the conductors of said line, other lines,and means for extending a connection from any one of said trunks to anyone of said other lines.

16. In a telephone system in which the terminals of the trunk lines arearranged in groups and in which the trunks in each group are furtherarranged in sub-groups, a line, conductors for said line, a circuitcloser for said line, a propelling mechanism for advancing said circuitcloser to a group of trunks, and for thereafter advancing the circuit,closer to a sub-group of trunks, test circuits for testing and formaking the trunks busy in the sub-group, means individual to saidcircuit closer controlled by said test circuits when all the trunks arebusy for rendering said mechanism inopera tive, a release deviceassociated with said mechanism for restoring the said mechanism tooperative condition, said test circuits being independent to theconductors of said line, other lines, and means for extending aconnection from any one of said trunks to any one of said other lines.

17. In a telephone system, an automatic progressively movable switch,trunk lines accessible to said switch, said trunk lines divided intogroups, a controlling relay for said switch, an operating mechanismcontrolled by said relay to elect a group of said trunks, the electedgroup divided into subroups of trunks, said mechanism controlled y saidrelay for electing a sub-group of trunks, busy test circuits associatedwith the trunks of said sub-group for automatically operating saidmechanism until an idle trunk in said sub-group is found, an auxiliaryrelay in said switch and an auxiliary circuit associated with saidsub-group for operating said relay to render the said mechanisminoperative to select trunks if all the trunks of the sub-group arebusy, other lines, and means for extending a connection from any one ofsaid trunks to any one of said other lines.

18. In a telephone system, an automatic progressively movable switch,trunk lines accessible to said switch, said trunk lines divided intogroups, a controlling relay for said switch, an operating mechanismcontrolled b said relay to elect a group of said trun (S, the electedroup divided into sub-groups of trunks, said mechanism controlled bysaid relay for electing a subgroup of trunks, busy test circuitsassociated with the trunks of said sub-group for automatically operatingsaid mechanism until an idletrunk in said sub-group is found, anautomatic switch associated with the selected trunk, a. control circuitfor said last switch comprising a section individual to the first switchand under the control of said relay, and a section individual to theselected trunk, said mechanism operating to bring the two together whenan idle trunk is found, whereby the switch in the selected trunk may becontrolled by the said relay.

19. In a telephone system, a line, an impulse sender associated withsaid line, an automatic progressively movable switch for said line,trunk lines associated with said switch, said trunk lines divided intogroups, an operating mechanism for said switch, a control relayassociated with said line to respond to said impulse sender, saidmechanism controlled by said relay in response to said sender to elect agroup of trunks and also to elect a sub-group of trunks, an auxiliarycircuit for energizing said mechanism after the impulse sender hasceased sending impulses to automatically operate to select an idle trunkin the elected sub-group, means for maintaining said auxiliary circuitin operative as long as the switch is operating to elect a sub-group,other lines, and means for extending a. connection from any one of saidtrunks to any one of said other lines.

20. 111 a telephone system, a line, an impulse sender associated withsaid line, an automatic progressively movable switch for said line,trunk lines associated with said switch, said trunk lines divided intogroups, an operating mechanism for said switch, a control relayassociated with said line to respond to said impulse sender, saidmechanism controlled by said relay in response to said sender to elect agroup of trunks and also to elect a sub-group of trunks, an auxiliarycircuit for energizing said mechanism after the impulse sender hasceased sending impulses to automatically operate to elect an idle trunkin the elected sub-group, and a slow-acting device for maintaining saidauxiliary circuit inoperative as long as the switch is operating toelect a sub-group, other lines, and means for extending the connectionfrom any one of said trunks to any one of said other lines.

21. In a telephone system. a line, an impulse sender associated withsaid line, an automatic progressively movable switch for said line,trunk lines associated with said switch, said trunk lines divided intogroups, an operating mechanism for said switch, a control relayassociated with said line to respond to said impulse sender, said meclranism controlled by said relay in response to said sender to elect agroup of trunks and also to elect a sub-group of trunks, an auxiliarycircuit for energizing said mechanism after the impulse sender hasceased sending impulses to automatically operate to select an idle trunkin the elected sub-group, and a slow acting magnet for maintaining saidauxiliary circuit inoperative as long as the switch is operating toselect a subgroup, other lines, and means for extending the connectionfrom any one of said trunks to any one of said other lines.

22. In a telephone system in which the terminals of the trunk lines arearranged in groups and in which the trunks in each group are furtherarranged in sub-groups, a line, a circuit closer for said line, apropelling mechanism for advancing said circuit closer to a roup oftrunks, and for thereafter advancing the circuit closer to a sub-groupof trunks, means for making a trunk busy in the sub-group, saidmechanism controlled by said means to automath-ally advance the circuitcloser in the sub-group until a non-busy trunk is found, meanscomprising said circuit closer for connecting the line and the non-busytrunk, an inductive device associated with the circuit closer fordividing the established circuit between the said line and trunk intotwo sections, an impulse sender associated with the line side of thedivision, and an im ulse receiving and repeating device associated withthe circuit closer and responsive to the impulse sender to repeatimpulses to the trunk side of the division.

:23. In a telephone system in which the terminals of the trunk lines arearranged in groups and in which the trunks in each group are furtherarranged in sub-groups, a line, a circuit closer for said line, a propelling mechanism for advancing said circuit closer to a group oftrunks, and for thereafter advancing the circuit closer to a subroup oftrunks, means for makin a trun bus in the sub-group, said mechanismcontroller? by said means to automatically advance the circuit closer inthe sub-group until a non-busy trunk is found, means comrising saidcircuit closer for connecting the line and the non-busy trunk, aninductive device associated with the circuit closer for dividing theestablished circuit between the said line and trunk into two sections,an impulse sender associated with the line side of the division, and animpulse receiving and repeating device associated with the circuitcloser and responsive to the impulse sender to repeat impulses to thetrunk side of the divislon, said impulse receiving and repeating devicehaving a line relay connected with the line for receiving the impulsesfrom the impulse sender over both sides of the line in series.

24. In a telephone system in which the terminals of the trunk lines arearranged in groups and in which the trunks in each group are furtherarranged in sub-groups, a line, a circuit closer for said line, apropelling mechanism for advancing said circuit closer to a group oftrunks, and for thereafter advancing the circuit closer to a sub groupof trunks, means for making a trunk bus in the sub-group, said mechanismcontrolled by said means to automatically advance the circuit closer inthe sub-group until a non-busy trunk is found, means comprising saidcircuit closer for connecting the line and the non-busy trunk, aninductive device associated with the circuit closer for dividing theestablished circuit between the said line and trunk into two sections,an im- 1,81B,lb8

pulse sender associated with the line side of the division, and animpulse receiving and repeating device associated with the circuitcloser and responsive to the impulse sender to repeat impulses to thetrunk side of the division, sai impulse receiving and repeating devicehavin a line relay connected with the line for reoe vin the impulsesfrom the impulse sender over th sides of the line in series and forrepeating said impulses to the trunk.

25. In a tale hone trunking system in which the termlnals of the trunklines are arranged in groups and in which each group is further arrangedinto sub-groups, a line, conductors for said line, an automaticprogressively movable switch, said switch controlled o-ver the line toelect a group of trunks and thereafter to elect a sub-grou p of trunkstherein, test circuits for said trunks and switch, means in said testcircuits indi vidual to said switch for controlling the switch to insureits advancement from busy trunk to busy trunk automatically until anidle trunk is found, said test circuits being independent of theconductors of said line, and an auxiliar circuit whereby if all thetrunks in the su group are busy the switch is prevented from passing tothe next subgroup, other lines, and means for extending a connectionfrom any one of said trunks to any one of said other lines.

26. In a telephone trunking system in which the terminals of thetrunk'lines are arranged in groups and in which each group is furtherarranged into sub-groups, a line, conductors for said line, an automaticpro gressively movable switch, said switch controlled over the line toelect a group of trunks and thereafter to elect a subroup of trunkstherein, test circuits for sai trunks and switch, means in said testcircuits individual to said switch for controlling the switch to insureits advancement from busy trunk to busy trunk automatically until anidle trunk is found, said test circuits being independent of theconductors of said line, and an auxiliary circuit whereby if all thetrunks in a sub-group are busy the mechanism for advancing the switch isrendered inoperative to prevent the switch from passing to anothersub-group, other lines, and means for extending a connection from anypne of said trunks to any one of said other mes.

27. In a telephone trunking system in which the terminals of the trunklines are arranged in groups and in which each group is further arrangedinto sub-groups, a line, an automatic progressively movable switch, saidline indlvidual to said switch, said switch controlled over two sides ofthe line in series, to elect a group of trunks and thereafter to elect asub-group of trunks therein, test circuits for said trunks and switch,for controlling the switch to insure its :ulvancement from busy trunk tobusy trunk automatically until an idle trunk is found, other lines, andmeans for extending connection from any one of said trunk lines to anyone of said other lines.

it). In a telephone trunking system in which the terminals of the trunklines are arranged in groups and in which each group is further arrangedinto sub-groups, a line, an automatic progressively movable switch, saidline individual to said switch, said switch controlled over two sides ofthe line in series, to elect a group of trunks and thereafter to elect asub-group of trunks therein, test circuits for said trunks and switch,for controlling the switch to insure its advancement from busy trunk tobusy trunk automatically until an idle trunk is found, and an auxiliarycircuit whereby it all the trunks in the subgroup are busy the switch isprevented from passing to the next subgroup, other lines, and means forextending the connection from any one of said trunks to any one of saidother lines.

29. In a telephone trunking system in which the terminals of the trunklines are arranged in groups and in which each group is further arrangedinto sub-groups, a line, an autol'nz'rtic progressively movable switch,said line individual to said switch, said switch controlled over twosides of the line in series, to elect a group of trunks and thereafterto elect a sub-group of trunks therein, test circuits for said trunksand switch, for controlling the switch to insure its advancement frombusy trunk to busy trunk automatically until an idle trunk is found, andan auxiliary circuit whereby if all the trunks in a sub-group are busythe mechanism for advancing the switch is rendered inoperative toprevent the switch from passing to another sub-group, other lines, andmeans for extending the connection from any one of said trunks to anyone of said other lines.

30. In a telephone system, a plurality of trunk lines, a selector switchhaving a contact arm adapted to connect with any one of said trunks,means for operating said arm. means whereby said arm will not stop uponcertain of said trunks unless said trunks are idle, means whereby saidarm will stop upon other of said trunks whether they are idle or busy,means for preventing the establishment of a circuit over saidlastnientioned trunks if they are busy, all of said means having magnetsall of which are always energized by a current flow in the samedirection, other lines, and means for extending a connection from anyone of said trunks to any one of said other lines.

31. In a telephone system, a plurality of subscribers lines, meansincluding a group of trunks for establishing a connection between acalling and a called subscribe1"s line, an automatic switch forconnecting with said trunks, means whereby said switch will not stopupon certain of said trunks unless said trunks are idle, means wherebysaid switch will stop upon one of said trunks whether it is idle orbusy, means for giving a busy signal in case said switch stops upon atrunk that is busy, all of said means having magnets all of which arealways energized by a current flow in the same direction, other lines,and means for extending a connection from any one of said trunks to anyone of said other lines.

32. In a telephone system, a plurality of trunk lines, a selector switchadapted to connect with any one of said trunks, means whereby saidswitch will not stop upon cer tain of said trunks unless said trunks areidle, means whereby said switch will stop upon other of said trunkswhether they are idle or busy, all of said means having magnets all ofwhich are always energized by current flow in the same direction, otherlines, and means for extending a connection from any one of said trunksto any one of said other lines.

33. In a telephone system, an automatic switch, trunk lines accessibleto said switch divided into groups and sub-groups, means for operatingsaid switch to select a desired group and sub-group, automatic means foroperating said switch to select an idle trunk in a selected sub-group, abusy test relay individual to said switch and a circuit for said relayincluding a movable contact of said switch closed only when the switchin its automatic operation arrives at the last trunk in the sub-group.

34. In a telephone system, an automatic switch, trunk lines accessibleto said switch divided into groups and sub-groups, means for operatingsaid switch to select a desired group and subgroup, automatic means foroperating said switch to select an idle trunk in a selected sub-group,busy signaling mechanism, and separate test circuits for controllingsaid automatic means and said signaling mechanism.

36. In a telephone system, an automatic switch, trunk lines accessibleto said switch divided into groups and sub-groups, means for operatingsaid switch to select a desired group and sub-group, automatic means foroperating said switch to select an idle trunk in a selected sub-group,busy signaling mechanism, and separate test circuits for controllingsaid automatic means and said signalin mechanism, means for closing oneof said test circuits to test each trunk in the group and means forclosing the other test circuit to test only the last trunk in the cup.

36. In a. telephone system, an automatic switch, trunk. lines accessibleto said switch divided into groups and sub-groups, means for operatingsaid switch to select a desired grou and a desired sub-group in theselccte group, automatic means for operating said switch to pass overbusy trunk lines in the selected subgroup, a, grounded battery, acontrol relay connected to the ungrounded pole of said buttery, a testterminal for the last trunk in the selected sub-group grounded if saidtrunk is busy, and a circuit for said relay including said groundconnection closed by the switch when it reaches said last trunk, wherebythe said relay is operated to stop said switch.

37. In a telephone system, an autonn-itic switch, trunk lines accessibleto said switch divided into groups and sub-groups, means for operatingsaid switch to select a desired group and sub-group, test terminals forsaid trunk lines, means for connecting said tcrminals to round when the(,:orres1' o-1nling trunks are Ens), a grounded battery, controlmechanism in said switch connected to the ungrounded )ole of saidbattery, circuit con nections esra -lished :upon the selection of asub-group between said mechanism and successive ones of said testterminals, whereby said mechanism is operated by current from the groundconnections on busy test terminals to wntrol said switch to select anidle trunk and in case all the trunks are busy to stop said switch onthe last trunk.

38. In a telephone system, an automatic switch, trunk lines accessibleto said switch divided into groups and sub-groups, subscribe! controlledmeans for operating said switch to select a desired group and subgroup,teslt terminals for said trunk lines, means for connecting saidterminals to ground when the corresponding trunks are busy, a groundedbattery, control mechanism in said switch connected to the ungr-onndedpole of said battery, circuit connections established upon the selectionof a sub-group between said mechanism and successive ones of said testterminals, whereby said mechanism is operated by current from the groundconnections on busy lest terminals to control said switch to select anidle trunk and in case all the trunks are busy to stop said switch onthe last trunk and means efl'cetive in the latter instance fortransmitting a busy signal to the calling subscriber.

Signed by me at Chicago, (look county, Illinois, this 18th day ofOctober, 1911.

TALBOT G. MARTIN.

Vvitnesses:

ARTHUR J. RAY, EDWARD D. FALES.

Cqptu of this patent may "be obtained tor five cents each, by addressingthe Commissioner 0! Patents,

' Washington, D. 0.

